1. Field of the Invention:
The present invention relates to a surface layer of an interior article examples of which are the instrument panel, front and rear doors on both sides and the roof of an automobile.
2. Description of the Prior Art:
In a conventional interior material such as the instrument panel of an automobile, as shown in FIG. 5, a buffer layer 22 formed by a foam for example is bonded to the outer surface of a frame member 21, and a surface layer 23 formed of polyvinyl chloride resin and having a suitable hardness is bonded to the outer surface of the buffer layer 22. Further, on the surface of the surface layer 23 is formed a wrinkle pattern as an uneven pattern 24 expressing artificial leather cloth for imparting a soft feeling to the said surface.
In order to form the uneven pattern 24 on the surface of the surface layer 23, we have developed such a vacuum forming method as is disclosed in Japanese Patent Laid-Open No. 104848/86 wherein the uneven pattern 24 is formed simultaneously with a forming operation using a pattern die having a sheet lap surface formed with an uneven pattern corresponding to the uneven pattern 24 and also having innumerable, fine, continuous pores which are distributed uniformly throughout the whole of the said sheet lap surface. According to this method, a synthetic resin sheet with the buffer layer 22 bonded thereto is softened by heating at a high temperature beforehand onto the back of the surface layer 23, then the surface of the surface layer 23 is brought into close contact by suction with the pattern die positioned just thereabove to effect forming, whereby the uneven pattern 24 of the pattern die, e.g. a wrinkle pattern, is transferred onto the surface of the surface layer 23.
However, a portion of the surface layer 23, e.g. a bent portion, which is drawn out largely during the forming operation may be broken, or the uneven pattern 24 may become unclear due to variations in heating temperature for the synthetic resin sheet or due to drop in temperature of the synthetic resin sheet or variations in the said temperature drop during forming using the pattern die after the heating. And this tendency is more conspicuous in the drawn-out portion.